This invention relates to a method of installing plastic liners within pipelines, either initially or as repair, for protecting the internal walls of the pipelines from deterioration. The invention further relates to tubular plastic liners as installed in pipelines. For deteriorated or damaged pipelines the liner restores the fluid transporting capability of the pipelines and prevents further interior deterioration.
One method and a respective liner for protecting the interior of pipelines is disclosed by French Patent No. 81 07 346 to Laurent. In that patent, there is disclosed a cylindrical liner of plastic material having historic time memory properties, i.e., shape memory characteristics, the liner being deformed to a predetermined reduced overall diameter at an appropriate temperature. The deformed liner is introduced into the pipeline, and hot steam or fluid is forced into the liner sufficient to obtain an average crystallization temperature of the material so that the deformed liner assumes its original cylindrical shape. Pressure is then applied within the liner to conform the liner to the interior contour of the pipe.
Another method for installing a plastic liner within a pipe is described in British Patent Specification 1 580 438 or in the PCT application PCT/AU86/00362. This known method uses liners of semi-rigid plastics material, and provides the following steps: forceably mechanically collapsing the liner so as to form at least one longitudinally extending depression, fixing a longitudinally extending tearable strap to or about the liner so as to maintain the collapsed configuration, introducing the collapsed liner in its maintained collapsed configuration into the pipe for a desired distance along and within the pipe and releasing the strap in order to restore the tube to its original shape, thus making use of the spring rebounding effect of the liner material.
U.S. Pat. No. 5,034,180 discloses a method for installing a liner of plastic material in a pipe. The method of this patent uses a thin flexible tubular membrane providing a heat containment tube for insertion into and inflation within an underground conduit to be repaired. The thermally deformed liner is inserted into the tube while hot, and flexible. The tubular membrane is pressurized to exclude unwanted fluids from within the existing conduit. Then, hot steam is injected into the tube to heat the pipe for its full length externally and internally until it assumes its original circular shape, the liner being thereby expanded against the walls of the pipe, with a flexible tubular membrane therebetween.
All of these known methods rely on the thermal deformation or mechanical collapsing of the plastic liners, and to the respective restoration of the deformed liner in the pipe. These processes are restricted to liners which do not exceed a pre-given wall thickness and this affects the reliability of the lined pipe in some cases.
The present invention provides a multiple tubular liner arrangement of plastic material, including a cylindrical first tubular liner of deformable or collapsible plastic material, the external diameter of the first liner corresponding to the internal diameter of the pipe to be lined, and a cylindrical second tubular liner of deformable or collapsible plastic material for closely fitting into the first liner. Ribs extend radially between the inner surface of the first liner and the outer surface of the second liner for spacing the liners relative to each other.
The present liner-within-a-liner system is useful not only for rehabilitation of dilapidated pipelines but also in the installation of new pipelines. The benefit of introducing two liners in the pipe, with ribs extending radially between the two lines, includes the formation of longitudinally extending continuous holes between the inside of the first liner and the outside of the second liner or between adjacent liners when more than two liners are employed. These holes enable the insertion of a sensing system along the first liner to provide information concerning any failure of the inner liner. By inserting into the pipeline two liners with a rib-structure between the liners, a large wall thickness can be established with each liner having a comparatively thin wall thickness and a corresponding flexibility which facilitates installation of the liners into the pipes. Although there is avoidance of a massive wall and material use, the effective wall thickness is correspondingly increased. The holes provided by the rib-structure function as conveyors of potential problems which may exist in the pipeline.
In a preferred embodiment of the invention, at least one of the liners consists of plastic material, e.g., polyethylene, having shape, of historic time, memory properties. The liner is deformed at or above deforming temperature and below the crystallization temperature of the material. The deformed liner in the pipe is restored to its cylindrical shape by forcing hot steam or another hot fluid along the liner, the temperature of the steam or fluid being sufficient to obtain an average crystallization temperature of the plastic material so that the liner will restore to its circular cross-section and closely fit into the pipe.
When both liners consist of plastic material with shape memory properties, then both liners are deformed thermally and mechanically at or above the deforming temperature and below the crystallization temperature of the liners. Then, the restoration of the cylindrical shapes of both liners is realized by passing hot steam or fluid into the space between both liners. This processing has the benefit of reducing the volume of the necessary hot steam or liquid thereby reducing the steam or liquid requirement regardless of the size of the pipe and economizing the overall production costs.
To conform both liners to the interior contour of the pipe, pressurized air or liquid, i.e., fluid, is passed into the second liner after the liners are heated above their crystallization temperature. The second liner is thus pressed via the ribs against the first liner which closely conforms to the inner wall of the pipe.
To facilitate installation of the second liner, it may be preferable to first partially open the first liner after its installation in the pipe. To accomplish this, hot steam or fluid sufficient to obtain an average deforming or higher temperature of the plastic liner material or obtain sufficient opening of the first liner to receive the second liner, is forced into the first liner after its introduction into the pipe, and the steam may be pressurized to partially widen the cross-section of the first liner to facilitate the introduction of the second liner.
In a preferred alternative, one or both or all of the liners may comprise a semi-rigid plastic material. The liner(s) is collapsed by mechanical force so as to form at least one longitudinally extending depression. To maintain the collapsed configuration, a longitudinally extending tearable strap is fixed to or about the liners(s). The strap is torn off after the collapsed liner is introduced into the pipe or the first liner, respectively. As in all embodiments hereof, ribs extend radially between the inner surface of the first liner and the outer surface of the second liner, i.e., between the inner and outer surfaces of next adjacent liners. The ribs space the liners relative to each other. To restore the cylindrical shape of the liners, pressure may be exerted in the first and/or second liner or within all liners to support the spring rebounding effect by which inherent elastic spring forces bring the liner(s) back to its cylindrical cross-sections.
It is particularly preferred to secure the liners one to the other in a final step after the liners are--via the ribs--in intimate contact with each other. This securement can be made either by electro or heat fusion or welding, by gluing, bonding or mechanically snapping. This integral connection of the liners results in a high strength compound liner structure having a large effective wall thickness with corresponding rigidity and strength, and yet the structure avoids the massive walls end corresponding amount of material, and simultaneously provides longitudinally extending holes or voids between the rib-structure which allows permanent failure control of the liners. For example, by a fiber optic sensing system introduced into the longitudinal holes, it is possible to instantly detect and locate leaks. Thus, where, for example, two liners are employed, the present invention enables double containment protection for the pipe, large effective wall thickness affording high strength and avoids disadvantages associated with minimum material and wall thickness due to the rib-structure of the integrally connected first and second liners.
Preferably, fusion of the two liners is an electrofusion with wires embedded in the contact areas of the liners running in the longitudinal direction of the liners from one end to the other. The wires are energized by electrical energy when the fusion is to be carried out.
As an alternative, electrofusion may be accomplished by using plastic material with electroconductive resistive contact zones or having ultra-high molecular weight polyethylene added to the plastic material, the liners being electrofused when contacting each other due to the electroconductive properties of the added ultra-high molecular weight polyethylene.
As another preferred alternative, the fusion of the two liners may be accomplished by passing hot steam or hot fluid through preformed fusion channels. The channels are preferably formed at the contacting areas of the liners, for example, at the free ends of ribs, the channels running in the longitudinal direction of the liners. The temperature of the fluid is sufficient to cause the plastic material of the ribs to fuse with the liner.
In another preferred embodiment of the invention, the two liners are glued or bonded together at their contact areas. Beads of hot melt adhesives are preferred for gluing the liners together and may be provided along the outer edges of the ribs. Hot steam is passed into the liners, having a temperature sufficient to activate the adhesive.
The ribs between the liners may be integrally formed, for example, in the case of two liners, at the inner surface of the first liner and/or at the outer surface of the second liner. The ribs extend preferably in the longitudinal direction of the liners, In alternative forms, the ribs may extend in circumferential or helical directions around the liners.
Preferably, the ribs have rectangular, trapezoidal or partly cylindrical cross-sections. The ribs may also be intermittently arranged to provide an interface between rib-created voids. As the free ends of the ribs contact the outer surface of the second liner and the inner surface of the first liner, respectively, the fusion means, for example embedded wires or beads of hot melt adhesive, are embedded at the free end of the ribs. Additionally, small channels are provided in longitudinal direction at the free ends of the ribs for passing hot steam or fluid through the channels to fuse the free ends of the ribs of one liner to the contacting surface of the other liner or to liquefy the hot melt adhesive and hence adhesively bond the liners to one another.
In a preferred step, a curing compound is molded or injected into the grooves between the liners if additional strength and material is required. As filler material, fly ash, perlite or expanded stearine are preferred, but other suitable compounds may be used as well.
Further, where three liners are used, the third cylindrical liner may be introduced into the second liner in the same way as the second liner is introduced into the first liner. This increases the effective wall thickness to an even greater extent. A rib-structure is similarly provided between the third and second liners. Also, the third liner may be integrally fixed to the second liner at the free ends of the ribs to enhance the strength and the lining properties.
In a preferred embodiment according to the present invention, there is provided a method of lining a pipe, comprising the steps of providing a first tubular liner of plastic material deformed from a generally cylindrical shape having an external diameter corresponding generally to the internal diameter of the pipe to be lined to a reduced diameter enabling reception of the deformed lining in the pipe, providing a second tubular liner of plastic material deformed from a generally cylindrical shape having a predetermined external diameter to a reduced diameter enabling reception of the second liner in the first liner, providing ribs between the inner surface of the first liner and the outer surface of the second liner for spacing the liners relative to each other in the pipe, introducing the first deformed liner into the pipe, introducing the second deformed liner into the first liner and restoring the deformed liners while in the pipe to their respective cylindrical shapes to enable the first liner to bear against the internal surface of the pipe and the first and second liners to contact one another by way of the ribs.
In a further preferred embodiment according to the present invention, there is provided a lining system for a pipe comprising a first tubular liner of plastic material deformed from a generally cylindrical shape having an external diameter corresponding generally to the internal diameter of the pipe to a reduced diameter enabling reception of the deformed liner in the pipe, a second tubular liner of plastic material deformed from a generally cylindrical shape having a predetermined exterior diameter to a reduced diameter enabling reception of the second liner in the first liner, the deformed first and second liners being reformable into the cylindrical shapes, respectively and a plurality of ribs carried by one of the first and second liners and extending radially between the inner surface of the first liner and the outer surface of the second liner for spacing the liners relative to each other when the liners are reformed into their respective cylindrical shapes in the pipe.
In a further preferred embodiment according to the present invention, there is provided a lining system for a pipe comprising a first tubular liner of plastic material having a generally U-shaped cross-section enabling reception of the U-shaped liner in the pipe, a second tubular liner of plastic material having a generally U-shaped cross-section enabling reception of the second generally U-shaped liner in the first liner, the first and second liners being reformable from their respective generally U-shaped cross-sections into generally cylindrical shapes, respectively, and a plurality of ribs carried by one of the first and second generally U-shaped liners and projecting between the inner surface of the first liner and the outer surface of the second liner for spacing the liners relative to each other when the liners are reformed into their respective cylindrical shapes in the pipe.
It is therefore a general object of the present invention to provide a method for installing plastic liners in a pipe, wherein the method increases the reliability, safety and risk control of the lined pipe.
It is a further object of the present invention to provide a tubular plastic liner arrangement with increased reliability, safety and risk control as compared with known liners.
These and further objects and advantages off the present invention will become more apparent upon reference to the following specification, appended claims and drawings.